Adjustable wrench



Sept. 1, 1936. A P [BBOTT 053,033

ADJUSTABLE WRENCH Filed March 11, 1935 2 Sheets-Sheefl A 22. rw

m f I: 17/ I: W f m Sept. 1, 1936. v ,A. P. lBBOTi' .ADJUS TABLE WRENCHFiled March 11, 1955 2 Sheds-Sheet 2 i a k 90 7/ I 2 law 70/? Hem w? I?155077 Patented Sept. 1, 1936 PATENT OFFICE ADJUSTABLE WRENCH ArthurPearson Ibbott, Oxhey, Hertfordshire,

. England Application -March 11, 1935, Serial No. 10,556

2 Claims.

This invention is directed to an improvement in wrenches and is filed asa continuation in part of my application Serial No. 653,696, filedJanuary 26, 1933. The improved wrench is of the adjustable typeinvolving a fixed jaw and a movable jaw, the adjustment between the jawsto:grip an object being obtained through the manual operation of a camforming part of the wrench structure.

In wrenches of this type it is of primary importance that the cam shouldshift the movable jaw through a maximum distance relative to the fixedjaw so that the wrench will have the widest possible range of jawsettings. It is further im- 15 portant that the angle between thedirection of thrust of the movable jaw upon'the cam and a tangent to thecam surface at the point of cooperation between the movable jaw and saidcam surface be such that the movable jaw is 20 held in its adjustedrelation to the fixed jaw, and

that rotation of the cam by the movable jaw incident to the pressure onsuch jaw in the use of the wrench is prevented. If the angle referred tois at any point of cam adjustment be- 25 yond a-safe angle, hereinafterreferred to as the critical angle, the cam will not hold the movable jawin its adjusted position, and thus the efiectiveness of the wrench willbe lost. If, however, the angle referred to be equal 'to, or less 30than, the critical angle, the cam will not slip under the pressure ofthe sliding jaw thereon and the wrench will be effective for allpositions within the limits of cam movement. It has been found that thiscritical angle is dependent upon 35 the size ofthe cam pivot, and that,in fact, it varies with the size of said'pivot, decreasing as the pivotis decreased. It will be clear that the smaller the critical angle thesmaller will be the range of jaw settings of the wrench. It is true .40that a cam of any desired throw can be obtained in'the case of any formof spiral cam by increasing the size of the latter, but, in consideringa .cam appropriate in size to the wrench with which it is associated,there is a decided limit to the 45 size of cam which it is practical touse, and hence the necessary throw brought about by the cam, and thusthe requirement of maximum cam-throw resulting from the form of camemployed must be determined with regard to the 50 ultimatesize of camwhich is appropriate for the wrench with which it is to be associated.

The primary object of the present invention, therefore, is to. provide acam appropriate to the wrench with which it is associated which shall 55.givethe maximum possible throw for its size and yet in all positions ofadjustment maintain a co-operating relation at somewhat less than thecritical angle.

The invention in its preferred form of detail is illustrated by theaccompanying drawings, of 5 which:

Figure 1 shows a wrench in elevation.

Figure 2 is a longitudinal section on the line 2-2 of Figure 1 drawn toan enlarged scale.

Figure 3 is a, longitudinal section of a wrench 10 drawn to the sameenlarged scale showing a slightly modified arrangement of parts, butotherwise constructed in accordance with the preferred form.

Figure 4 is a diagram showing, in addition to a cam of the presentinvention, three cams of ordinary spiral type; and, Figure 5 is adiagram showing in the upper partthereof lift obtained plotted againstlength of cam surface in the case of each of the four cams of Figure 4,and in the lower part thereof degrees of rotation plotted against lengthof cam surface in each of the four cams shown in Figure 4.

The wrench as illustrated comprises a handle I having a fixed jaw 2 atone end thereof. A sliding jaw 3 is provided with an elongated sleevesection 4 which slidably embraces the handle and accurately guides themovement of the movable jaw toward and from the fixed jaw. Mounted onthe handle through the medium of a pivot 5 is a cam 6, both pivot andcam being of particular construction and arrangement, as willhereinafter be more specifically referred to.

In the form shown in Figures 1 and 2 the cam directly engages the loweredge of the sleeve 4 so that as the cam 6 is turned in one direction thesleeve 4 and thereby the movable jaw is advanced towards the fixed jaw.A spring I, fixed at one end to a pin 8 seated in a longitudinal channel9 in the handle I, is engaged at its other end with the movable jaw, asindicated at 10, so that the movable jaw is compelled to follow the camin the inoperative movement of the latter that is to say, during openingmovement of the wrench.

The construction shown in Figure 3 is similar in all respects, exceptthat the spring 1 and the pin 8 are omitted, and that the cam 6 isformed at its inner face, that is the face next to the handle, with anedge flange H and the movable jaw is provided with a dependentprojection l2 having a lip l3 to engage beneath the flange ll. Throughthe medium of this lip 13 in its co-operation with the flange I l theinoperative movement of the cam 6 will cause the sleeve 4 and therebythe movable jaw to move away from the fixed The essential features ofthe present invention reside primarily in the form of the cam andsecondarily in the size of the pivot with respect to the cam. In orderthat the important details of the cam may be brought out, it isnecessary to describe the details of conventional spiral cams and topoint out particularly wherein the cam of the present invention differsfrom such spiral cams in order to avoid'exceeding the critical angleabove referred to while at the same in time maintaining the maximumpossible throw less than the critical angle and which for equal for thegiven size. 1

In Figure 4 there are represented in broken lines three cams of spiraltype, and in full lines the cam of the present invention. I known, aspiral or snail cam gives equal rise for equal degrees of rotation, butgives unequal rise for equal lengths of cam periphery. Referring toFigure 4, it will be clear that for successive 90 sectors in any onespiral cam the throw is the same, but the length of cam peripheryincluded is radically diiferent. Assuming, for example, that in the caseof the spiral cam designated SI the length of cam periphery in the firstsector 0-90 is of an inch, the length of cam periphery in the secondsector 90-180 will be'l e inches, and the length of cam periphery. inthe third sector l-270 will be 1% inches; expressing these measurementsin 32nds of an inch, the respective lengths of cam periphery are 28, 42,and 52. For each of these peripheral lengths, however, the cam causesthe same throw' of {-2 of an inch.

In Figure 5, lengths of cam periphery are plotted horizontally, andagainst these lengths there are plotted vertically in the upper half ofFigure 5 corresponding cam throws, whilst, in the lower half of Figure5, degrees of rotation are plotted vertically against the horizontallyplotted lengths of cam periphery; the resulting graphs correspondingwith the cams,- respectively, of Figure 4 being designated by the samereferences as are employed in that figure.

From a-consideration of Figures 4 and 5 of the drawings, it is apparentthat in the spiral'cam Si the angle between the direction in which anelement operated bears thereon and a tangent to the-cam surface at thepoint of engagement of said element therewith is at its. maximum, i; e.the cam surface is at its steepest, in the first sector 0-90. Thesteepness of the cam surface is at a maximum where the latter is nearestto the pivot ofthe cam and decreases from this point to the point wherethe surface is at its maximum distance from the cam pivot. The only partof the periphery of the cam SI which. is withinthe criticalangle isclosely in the neighbourhood of its maximum distance from the pivot.

If, a spiral cam has the same minimum distance from its pivot asthe camSI and is so designed as to be safe even at this region of its surface,then the cam designated S2 is obtained, but, as will be seen, the totalthrow of this cam'is .only about one half of the cam. SI. It will beclearthat the cam S2 is quite unnecessarilysafe, that is to say, itssteepness is, to an'unnecessarily large extent, below the criticalangle'throughout almost its entire length, i. e., except at its smallestdistance from the pivot.

By increasing the distance of the cam surface from its pivot, a snailcam is produced which will give the same throw as the cam SI and stillbe safe throughout its length, the cam designated As is well S3 isobtained. This cam is unnecessarily safe,

quit impracticable.

As previously stated, it is of importance. to

maintain the angle of the cam somewhat less than the critical angle andat the same time secure the maximum throw or rise of the cam for theparticular purpose for which the cam is intended, and it is, therefore,necessary that a cam be constructed which will at every point of itsperiphery maintain a more or less constant angle off steps of equallength on successive concentric circles of relatively slight constantincrease in diameter. This is the cam of the invention and isillustrated by a full line at I in Figure liof'the drawings (thecorresponding graph being a full line, designated by LinFigur'e 5. ofthe drawings). It will be seen that the cam I is of the same dimensionalorder and has substantially the same throw as the .u'nsafe'spiral camSI. The cam I gives equal throws for equal lengths of cam periphery andis .of constant steepnessior safety throughout its length. 'Note thatthe graph I in Figure 5 is a straight line. Because, of this, the cam Igives twice the throw of. the small spiral cam S2 (which isunnecessarily safe throughout almost its entire length) :and is veryconsiderably smaller than the large spiral cam S3 (which isunnecessarily safe throughout. substantially the whole of its length),the throw of the cam S3 being no greater than that of the cam I.

V In addition to the formation of the cam, an important detail of thepresent invention is the provision of the spring 1 shown in Figure Z'andconstituting the preferred form of the invention in this respect. Itwillbe understood that when the wrench is under operating pressure and closecontact therefore maintained between the sleeve of the slidingjaw andthe cam, such cam,-if the angle is correct as defined in the instantapplication, will not slip or rotate. In the ordinary mode of using; awrench of this type, however, it is usual to turn it through about 60for a hexagonal nut or for a square nut and then to remove the spannerand replace it on the succeedingfaces of the nut .toicomplete thetightening or loosening operation, as: the case may be.

This operation is, of course, repeated as often as is necessary in the.particular instance. Each time the wrench is released from the nut,'as'for example for anew grip, the cam is free from pres sure andtherefore free to rotate and, as a matter of fact, it does so rotateeither owing to the oscillatory movements to which it issubjected in theoperator's hands or to the unequal weights'of V thevarious portions. ofthe cam about its pivot.

In theuse of the spring, there is. inall positions of the sliding sleeveand movable jaw relative to the fixed jaw .a pressureiexerted by thespring between the sleeve and'cam'. This pressure 'is sufficient tomaintain the-'sleevetightly pressed against the camand thus the cam isnot free to rotate under its own unequally disposed weight but is heldin the desiredposithe wrenchin' a new position for a further-turn ingmovement does not necessitate any further adjustment of the cam. Thespring pressure will cause the sliding sleeve to engage the cam withsufiicient holding effect to prevent the possibility of cam movementunder its own weight.

Therefore, the wrench having once been adjusted to the nut may, in aconventional manner, be removed therefrom and reapplied thereto withoutfurther attention to the cam or its position, for the spring actsautomatically to maintain the adjustment and permit reapplication to thewrench without necessity of further cam movement or adjustment. This isa particularly important detail in connection with wrenches of this typeand in effect renders the wrench, when set, a rigid relatively fixedwrench relation between the fixed and movable jaws which will permitcontinued reuse of the wrench on the same nut or bolt without requiringany attention to the position or further control of the cam.

It has been previously stated that the relative diameter of the pivot,while a secondary factor, is nevertheless of importance in theparticular arrangement defined. In the wrench disclosed, it is apparentthat the resistance to friction is relied upon to prevent slip orbackward rotation of the cam. This resistance is presented chiefly atthe periphery of the cam but nevertheless is present in appreciabledegree at the bearing of the cam on its pivot. The friction incident tothe bearing of the cam on its pivot would naturally be greater on arelatively large bearing than on a relatively small bearing. Thediameter of the pivot 5 is materially larger than that which wouldordinarily be considered commercially appropriate to support a cam ofthe particular size employed, and it is found that, owing to theproportionately large friction at the bearing surface between the camand the pivot, the critical angle is, in fact, increased. In otherwords, the larger the pivot, the steeper the cam may be withoutexceeding the critical angle, or, the larger the pivot, the larger isthe throw which is obtainable with safety against slip during use of thewrench, and thus the use of a large pivot enables a larger range of jawsettings to be obtained.

The characteristically important features of the present invention,therefore, reside in the specific provision of a cam which in itsoperation provides the maximum rise or throw and which in its peripheralsurface presents at no point an angle exceeding the critical angle andwith such peripheral surface so formed that the angle of the cam isconstant throughout; together with a pivot having a relatively increasedbearing surface with respect to the cam in order to increase thefrictional resistance at this point to cam slip.

What is claimed to be new is:

1. An operating means for an adjustable wrench of the type including a,handle carrying a fixed jaw, a movable jaw slidable with respect to thehandle toward and from the fixed jaw, said operating means including acam pivotally supported on the handle and cooperating with and operatingthe movable jaw toward the fixed jaw, the cam being of constant throwtype with the jaw-engaging periphery of such curvature that the anglebetween the normal to said curvature at the point of contact of saidmovable jaw and cam, and the line of thrust of the movable jaw at saidpoint will be less than the critical angle at which pressure on themovable jaw will cause a retrograde movement of the cam, the said lineof thrust passing through the point of contact and the center ofrotation of said cam, the operating surface of the cam approaching thecritical angle with the minimum margin of safety against retrograde cammovement in order to insure the maximum possible throw of the cam andtherefore maximum possible movement of the movable jaw in each incrementof cam movement.

2. An operating means for an adjustable wrench of the type including ahandle carrying a fixed jaw, a sleeve slidable on and guided by thehandle, and a jaw on said sleeve, said operating means including a campivotally supported on the handle immediately below the sleeve, thehandle and cam occupying such relative positions as to permit the handlebelow the cam to be grasped by the hand and the cam operated by thefingers of such hand, the cam having a constant throw peripheral surfacecooperating with the edge of the sleeve, the said peripheral cam surfacebeing so designed that the tangent at each point of said surfaceintersects a line at right angles to the axis of the sleeve at an anglewhich is slightly less than the critical angle at which the cam would bemoved under pressure on the sleevecarried jaw in the operation of thewrench, the line of pressure of the movable jaw passing through thepoint of contact and the center of rotation of the cam, and means formaintaining the cam for pivotal movement and to increase the frictionalresistance to the cam movement to thereby provide a further safetymargin against retrograde cam movement under pressure on thesleeve-carried jaw in the use of the wrench.

ARI'HUR PEARSON IBBO'I'I.

